1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus that can form an image on a long sheet.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a uniformly-charged photoconductor (for example, a photoconductor drum) with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet through an intermediate transfer belt, followed by heating and pressurization for fixing, whereby an image is formed on the sheet.
It is known that, when a two-component developer is used in an electrophotographic image forming apparatus, an external additive is buried on the toner surface and removed from the toner in association with agitation of the toner and carrier in a developing device, thus degrading the toner. In particular, when a low-coverage image is continuously formed, toner is kept agitated in the developing device without being replaced, and consequently degradation of the toner is significant. When toner is degraded, charging performance is degraded and consequently image unevenness and image fogging may possibly be caused. In addition, when the toner concentration (the proportion of toner in two-component developer) cannot be properly controlled due to degradation of the toner, charging performance of the toner becomes further unstable, and consequently image fogging, toner scatter, or toner spilling may possibly be caused. In view of this, in general, toner refreshing intended to forcibly eject degraded toner and replace the degraded toner with new toner is performed (see, for example, Japanese Patent Application Laid-Open No. 2010-72168).
For example, in the case where images are formed on flat sheets, a toner image for ejecting the degraded toner (hereinafter referred to as “ejection toner image”) is formed on an image bearing member (a photoconductor in the case of the direct transfer scheme, or an intermediate transfer belt in the case of the intermediate transfer scheme) in a region between a toner image transferred to a preceding sheet and a toner image transferred to a succeeding sheet (i.e., between images), and then collected with a cleaning section for the image bearing member, thereby forcibly ejecting the toner. At this time, the difference between the amount of the degraded toner generated by the image formation and the toner consumption amount is formed as an ejection toner image, and ejected. The ejection toner image passes through the transfer section in a period after the preceding sheet passes through the transfer section and before the succeeding sheet reaches the transfer section (i.e., the interval between sheets), and therefore the ejection toner image is not transferred to the sheet.
However, in the case where an image is formed on a long sheet such as a roll sheet and a continuous sheet (continuous form sheet), it is difficult to form an ejection toner image between images to forcibly eject the toner unlike the case where images are formed on flat sheets. Specifically, since conveyance of the long sheet is required to be ensured during the image formation process, it is impossible to use a configuration in which the pressure contact between the image bearing member and the long sheet is released only at a time when the ejection toner image formed between images passes through the transfer section. As a result, the ejection toner image formed between images is also transferred to the long sheet, and the quality as a long product is significantly degraded when a plurality of successive images are produced as one printing material.